1. Field of the Invention
This invention relates to compositions including organic compounds containing sulfur and to a method of forming higher molecular weight products from such compositions. This invention also relates to elastomers and resins consisting of organic polymers containing sulfur.
2. Description of the Prior Art
Compositions consisting of mercapto-functional organic compounds which are free of aliphatic unsaturation such as vinyl and are polymerized or cured by means of the mercapto groups are well-known in the art. Many types of curing or condensing agents have been suggested such as inorganic peroxides such as alkali metal and alkaline earth metal peroxides such as sodium peroxide or lead peroxide; inorganic oxidizing agents such as chromate or permanganate salts; organic peroxides such as benzoyl peroxide; organic hydroperoxides such as cumene hydroperoxide and other organic curing agents such as polyepoxides, polyisocyanates, organic borates or organic titanates; and the like, many of which are detailed in U.S. Pat. Nos. 2,466,963 and 2,964,503.
Room temperature polymerization or cure of such compounds, which is believed to be caused by oxidation resulting from exposure to air or oxygen, has been accomplished through the use of inorganic chromates such as sodium chromate, paint driers and heavy metal salts such as lead naphthenate or cobalt 2-ethylhexoate.
Nametkin, et al., in the Journal of Organometallic Chemistry, 149, pp. 355-370 (1978) report that when stoichoimetric amounts of Fe(CO).sub.5, Fe.sub.2 (CO).sub.9, or Fe.sub.3 (CO).sub.12 are reacted with thiols of the general formula RSH, where R is an alkyl or aryl radical, in solution, a complex {RSFe(CO).sub.3 }.sub.2 and a small amount of the disulfide, RSSR, is produced at room temperature and that Fe.sub.3 (CO).sub.12 is the most effective catalyst. Thermal decomposition of the complex in n-dodecane solution at 160.degree. C. in the presence of air results in decomposition of the complex to form the disulfide. However, this article does not teach that Fe(CO).sub.5, Fe.sub.2 (CO).sub.9 or Fe.sub.3 (CO).sub.12 will function as a catalyst in non-stoichiometric amounts for the room temperature polymerization or cure of the compositions hereinafter described nor does it suggest that the acids hereinafter described will accelerate the rate of surface polymerization or cure of such compositions.
Gary R. Homan and Chi-long Lee are the applicants named in U.S. patent application Ser. No. 099,282 filed on Dec. 3, 1979 pending entitled "Oxygen-Curable Mercapto-Functional Organic Compound Compositions Catalyzed by Metal Carbonyl Compounds And Method of Forming Higher Molecular Weight Products Therefrom" which is assigned to the same assignee as the present invention. In that patent application, Homan and Lee teach that the use of metal carbonyl compounds, especially those containing iron such as iron pentacarbonyl, in mercapto-functional organic compounds containing an average of at least two mercapto groups per molecule results in compositions which are storage stable in the absence of oxygen. Such compositions polymerize or cure at room temperature upon exposure to oxygen to a thickness of 0.5 millimeters after 24 hours and up to 3 millimeters after several weeks. Such products are useful as coatings, impregnants for porous materials and elastomeric sealants.
Quite unexpectedly, it was discovered that when an acid which satisfies the criteria set out below was included in iron carbonyl catalyzed compositions as taught by Homan and Lee, the composition exhibited a much faster rate of surface polymerization or cure than did compositions without an acid. Such improved compositions are especially useful where thin films are coated on articles such as wire, paper or electronic circuit boards because the rapid cure enables the articles to be handled at an earlier time than compositions which do not contain acid accelerators. Rapid surface cure also reduces the amount of time the surface is tacky and thus vulnerable to contamination by dust or other foreign matter.